Isomerisation of gas-phase structures with Coulomb explosion imaging.

该项目福尔斯EPSRC“化学反应动力学和机制”领域，并有助于“光物质相互作用和光学现象”和“计算和理论化学”。这项工作符合EPSRC“生产性国家”的繁荣成果。库仑爆炸成像是在20世纪80年代发展起来的;通过发射小分子穿过薄的固体膜，它表明它们可以被剥离电子，导致随后由于静电排斥而爆炸成带电碎片。激光技术的发展导致了20世纪90年代对库仑爆炸的兴趣的复苏，因为基本的电离过程可以通过与激光脉冲的电场的相互作用而容易地获得。随着X射线自由电子激光器（XFEL）的发展，人们对强场-物质相互作用的兴趣再次增加。这些现代技术在化学反应动力学方面产生了特别有趣的结果，因为这种脉冲持续时间与分子动力学在相同的时间尺度上。这些仪器的可调谐性允许控制许多反应参数，例如选择性地将核和电子波包促进到期望的状态和潜在表面，以及操纵反应时间依赖性。泵浦-探测程序允许操作员激发（和传播），并库仑爆炸分子系统与两个各自的激光脉冲的能量选择访问特定的反应机制。脉冲之间的时间可以变化，以可视化反应机制的时间演变。该项目将应用超快桌面和XFEL技术来了解气相异构体的化学反应动力学，改进质谱技术，并增加对复杂和复杂的光物质相互作用的基本理解。目前的质谱分析方法受到其无法区分结构异构体的限制，因此，几乎无法推断化学演变的阶段。通过使用泵探测和延迟技术进行异构化反应，可以将分子结构的显著变化解析为时间的函数，从而丰富了对分子在结构异构体之间转变的方式的理解。这项工作将集中在激光诱导的卤素间消除二卤代甲烷（CH 2X2，其中X代表卤素），其中看到的两个卤素取代基之间的键的形成，然后作为一个双原子卤素物种弹出。该过程预期在这种甲烷衍生物的液相中进行，并且理论上预期在气相中进行。证实或纠正这些预测的实验证据是新颖的。超快技术将用于跟踪键的形成和断裂机制，并分离和鉴定二卤代甲烷的气相异构体。所产生的片段的特性将被用来解释这些结构中的分子内卤素相互作用。进一步的工作将形成一个案例研究的CF2 X2系列的计算预测进行interhalo消除更容易比他们的CH 2X2对应。桌面和XFEL技术的使用，允许选择性地访问不同的电子状态的分子，将不仅允许结构异构体的分化，而且还增加了对基态和激发态贡献的理解。通过将核间分离可视化为时间的函数，可以对势能面与电子和核布居之间的复杂关系进行推断，并且可以通过收集的经验和实验数据来改进理论理解。分离和确认结构异构体的存在是有机和生物化学合成的重要目标。

This project falls within the EPSRC 'Chemical Reaction Dynamics and Mechanisms' area, as well as contributing to 'Light Matter Interactions and Optical Phenomena' and 'Computational and Theoretical Chemistry'. This work aligns with the EPSRC 'Productive Nation' prosperity outcome. Coulomb explosion imaging was developed in the 1980s; by firing small molecules through thin solid films, it was shown that they could be stripped of their electrons, causing subsequent explosion into charged fragments due to electrostatic repulsion. Developments in laser technology lead to a resurgence of interest in Coulomb explosions in the 1990s since fundamental ionisation processes could be easily accessed through interactions with the electric field of the laser pulse. The current accessibility of x-ray free electron lasers (XFEL) has once again been followed by an increased interest in strong field-matter interactions. These modern techniques yield particularly interesting results with respect to chemical reaction dynamics as such pulse durations are on the same timescale as molecular dynamics. The tunability of these instruments allow control of many reaction parameters, such as selectively promoting nuclear and electronic wave-packets to desired states and potential surfaces, and manipulating reaction time dependencies. Pump-probe procedures allow the operator to excite (and propagate), and Coulomb explode a molecular system with two respective laser pulses with energies selected to access specific reaction mechanisms. The time between pulses can be varied to visualise the time evolution of a reaction mechanism. This project will apply ultrafast table-top and XFEL techniques to understand the chemical reaction dynamics of gas phase isomers, improve upon mass-spectrometry techniques, and add to the fundamental understanding of complex and convoluted light-matter interactions. Current mass spectrometry methods are limited by their inability to differentiate between structural isomers and, as a result, allow little to be inferred about the stages of a chemical evolution. By following isomerisation reactions with pump-probe and delay techniques, significant changes in molecular structure can be resolved as a function of time, allowing an enriched understanding of the way molecules transition between structural isomers. This work will focus on laser-induced interhalogen elimination of di-halogenated methane (CH2X2, where X represents a halogen), which sees the formation of a bond between the two halogen substituents which are then ejected as a diatomic halogen species. This process is expected in the liquid phase of such methane derivatives, and theoretically expected for the gas-phase. Experimental evidence confirming or correcting these predictions is novel. Ultrafast techniques will be used to follow the bond formation and breaking mechanisms and to separate and identify the gas-phase isomers of di-halogenated methane. The characteristics of the fragments produced will be used to explain the underlying intramolecular halogen interactions in these structures. Further work will form a case study on the CF2X2 series which-computationally-are predicted to undergo interhalogen elimination more readily than their CH2X2 counterparts. The use of both tabletop and XFEL techniques, allowing selective access to different electronic states of a molecule, will not only allow the differentiation of structural isomers, but also add to the understanding of ground and excited state contributions. By visualising internuclear separation as a function of time, inferences may be made on the complex relationships between potential energy surfaces and electronic and nuclear population, and theoretical understanding may be improved upon through collected empirical and experimental data. Separating and confirming the presence of structural isomers is an important aim for organic and biochemical synthesis.